1. Field of the Invention
The present invention relates to a nonreciprocal circuit device and a communication apparatus including a nonreciprocal circuit device.
2. Description of the Related Art
An isolator disclosed in Japanese Unexamined Patent Application Publication No. 2001-136006 is known as a conventional isolator. As shown in FIG. 12, an isolator 200 includes an upper metal casing member 201, a permanent magnet 202, a center electrode assembly 203, a multilayer substrate 204, an external-connection terminal component 205, and a lower metal casing member 207. Reference symbol R indicates a resistance element. The center electrode assembly 203 and the multilayer substrate 204 are accommodated in the external-connection terminal component 205, and on the upper surface of the structure, the resistance element R and the permanent magnet 202 are arranged. The permanent magnet 202, the center electrode assembly 203, the multilayer substrate 204, the external-connection terminal component 205, and the resistance element R are then accommodated in the upper metal casing member 201 and the lower metal casing member 207, thereby defining a nonreciprocal circuit. In this case, to connect external-connection terminals 209 of the external-connection terminal components 205 to a mounting substrate, a groove 206, which has substantially the same depth as the thickness of the bottom section 208 of the lower metal casing member 207, is formed at the lower surface of the external-connection terminal component 205.
Since the isolator 200 requires the external-connection terminal component 205 as an individual component for connecting the external-connection terminals 209 to a mounting substrate, the cost of the isolator 200 is increased.
Another isolator disclosed in Japanese Unexamined Patent Application Publication No. 5-304404 is also known. As shown in FIG. 13, an isolator 300 includes a metal casing 301, a permanent magnet 307, a multilayer substrate 303 having a center electrode assembly therein, and a ferrite element 305. Side surfaces of the multilayer substrate 303 are provided with external-connection terminals 306 for connection with a mounting substrate. The isolator 300 is constructed such that the permanent magnet 307 and the ferrite element 305 are accommodated in the multilayer substrate 303, and the resulting structure is inserted into the metal casing 301. In this case, the lower portion 302 of the metal casing 301 fits into a groove 304 of the multilayer substrate 303. Thus, the multilayer substrate 303 has a cavity structure.
An isolator disclosed in Japanese Unexamined Patent Application Publication No. 9-55607 is also known as having a structure similar to that of the isolator 300.
For such an isolator 300, it has been difficult to manufacture such a multilayer substrate 303, which is obtained by firing and has a cavity structure with a large hole in the center thereof, with high accuracy at a low cost.
In order to overcome the problems described above, preferred embodiments of the present invention provide a nonreciprocal circuit device and a less-expensive communication apparatus with a reduced number of components.
According to a preferred embodiment of the present invention, a nonreciprocal circuit device includes
(a) a permanent magnet;
(b) a center electrode assembly that includes a ferrite element, to which a direct-current magnetic field is applied by the permanent magnet, and a plurality of center electrodes, arranged on a major surface of the ferrite element;
(c) a multilayer substrate that has a first major surface and a second major surface opposing the first major surface and that includes matching capacitor elements connected to corresponding ends of the center electrodes, in which the center electrode assembly is arranged on the first major surface and a plurality of external-connection terminal electrodes is provided at the second major surface; and
(d) a metal casing that encloses the permanent magnet, the center electrode assembly, and the multilayer substrate; and
(e) the metal casing is partially provided on the second major surface of the multilayer substrate, and at least one of the plurality of external-connection terminal electrodes protrudes from the second major surface by an amount measurement that is substantially equal to the thickness of the metal casing. In this case, preferably, the height of the protrusion of the external-connection terminal electrode from the second major surface is in the range of about 0.1 mm to about 0.2 mm.
Preferred embodiments of the present invention, therefore, can provide the terminals with sufficient flatness, and the user can directly solder the external-connection terminal electrodes of the multilayer substrate to a mounting substrate, which can eliminate an external-connection terminal component that has been conventionally required. In addition, this arrangement can eliminate the need for forming a large hole in the center of the multilayer substrate, so that the multilayer substrate can be fired in a plate state, thereby suppressing the deformation of the multilayer substrate and increasing the dimensional accuracy thereof. This further offers advantages in that the dimensional accuracy of the multilayer substrate is increased and the fabrication process of the multilayer substrate can be greatly simplified, which therefore can provide a high-performance and less-expensive nonreciprocal circuit device.
Preferably, the at least one external-connection terminal electrode that protrudes from the second major surface by an amount that is a substantially equal to the thickness of the metal casing fits into a notch provided in the metal casing. With this arrangement, the multilayer substrate and the metal casing can be easily positioned.
Preferably, the second major surface of the multilayer substrate has a ground electrode arranged to cover substantially the entire second major surface and the ground electrode is electrically connected to the metal casing. This arrangement allows for a sufficient contact area between the ground electrode and the metal casing, thus improving the electrical characteristic of the nonreciprocal circuit device.
The external-connection terminal electrodes that protrude from the second major surface by an amount that is substantially equal to the thickness of the metal casing may be only an input terminal electrode and an output terminal electrode. In this case, the ground terminal electrode is soldered to the mounting substrate via the metal casing. Since the area of the interface at which the metal casing and the mounting substrate are joined is large, this arrangement can improve the mounting strength of the nonreciprocal circuit device. Further, the majority of thermal stress and mechanical stress is applied to an interface at which the metal casing and the mounting substrate are joined, thereby alleviating the stress applied to the interface between the input and output terminal electrodes and the mounting substrate. This also can improve reliability in the connection of the input and output terminal electrodes.
A second preferred embodiment of the present invention provides a communication apparatus. The communication apparatus includes the nonreciprocal circuit device constructed according to the preferred embodiment described above. Thus, the communication apparatus offers the same advantages as those of the nonreciprocal circuit device according to other preferred embodiments of the present invention, thus allowing for a reduction in the manufacturing cost and an improvement in the electrical characteristic.
Other features, elements, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention with reference to the attached drawings.